[Heathkit] RE: SB-610?

[ma.locksmith at juno.com]

How does the amplitude on V4A plate compare with the amplitude on V4B
plate?

This sounds just like low gain in V4A.

While the schematic does show the grid resistor to be 270 K, the other
one IS 220 K.  I might guess a typo on the schematic....  but it
certainly shouldn't cause what you see.

However, a change in value of the cathode resistance or the bypass
capacitor being open would.

Ed


On Mon, 19 Feb 2007 19:09:30 +0000 "ehertz" <ehertz at tcaf.org> writes:
> Hello all!
> 
> Update on the 610 single tone output. Through careful and time 
> consuming tracing, I located one faulty soldering joint. The join 
> allowed B+ to get to the plate of V4B but not V4A! I was very luck 
> and thrilled to have located this fault. I resoldered and things are 
> slightly improved...
> 
> Now, while watching the tone output on a scope: When I go from "off" 
> to "1.5 KHz tone" I see a *momentary* sinewave on the scope. It then 
> seems to fade to zero in about 1/2 second or less. Every time I go 
> from off to 1.5 I see that momentary sinewave.  
> 
> So it seems the signal may be being dampened out and continuous 
> oscillation is not occurring.  So I kept looking...
> 
> I believe I located an incorrect component value.  Seems the 
> resistor from the first grid of V4A (pin 5) is supposed to be 270K. 
> On my unit, it appears to be 220K.  Can anyone confirm that this 
> could in fact be preventing this from oscillating?  If the answer is 
> no, I'd rather keep looking and leave that there. Its really burried 
> under a ton of other components. 
> 
> Any insight appreciated. thanks!
> Eugene
> 
> 
> 
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